The present invention relates to a steering wheel for motor vehicles and having a rim and depressed hub above which is disposed a restraining device for impact protection, through absorbtion and dissipation of impact shock.
Restraining and protection devices arranged in the steering wheel are specifically designed to protect the driver of a car, when not having the seat belts fastened, against injuries in the case of a collision at low or medium speeds. The restraining device in the steering wheel will not only protect the upper part of the body, particularly the chest of the driver, but should also prevent his head from being thrown against the windshield. If the driver has the seat belts fastened, the restraining device is particularly of interest for collision at medium and high speeds, avoiding injury through the seat belts particularly when strained up to the limit of elastic extension. Particularly in the latter case the driver's head could still hit e.g. the steering wheel unless the restraining device intercepts the motion of the head towards the wheel rim.
Shock energy absorbing and dissipating devices are known in considerable varieties as part of the effort to provide for passively working protection of the driver. For example, impact absorbers are disposed between steering wheel and column, and the hub is frequently cushioned by means of rather thin foam parts. One has also tried to place cylindrical, metallic elements on the hub, which elements may be deformed rather easily, but not too easily, so that deformation, even crushing, does absorb impact energy. These elements are additionally provided with a foam cover.
Other types of steering wheels have several rims, arranged one above another and connected to the hub so that upon impact they undergo deformation in particular sequence for sequentially dissipating the impact shock. Other energy dissipating devices have mushroom-shaped configuration and are of laminated construction with several, differently stiff, plastic lamina for energy dissipation and absorbtion. Another proposal relates to dish-shaped steering wheels wherein a thick and large impact absorber made of cellular material is disposed in the dish.
All these various devices are deficient in one way or another and do not provide adequate protection nor do they prevent injuries with a sufficient degree of certainty.
We have discovered that one of the reasons for the inadequate protection afforded by the known devices is to be seen in the orientation of the impact surface of the protecting device in relation to the most likely direction of impact by a body part of the driver. Ideally, the latter direction should be at right angles particularly in the instant of impact. In such a case, the body part would engage the surface of the restaining device immediately over a large area, and the interaction between the body part and the device while causing deformation of the device over a large zone, would not dangerously react against the body part in a localized, focusing effect. This case can be regarded as constituting the most favorable bio-mechanical situation for alleviating the danger of injury.
However, the situation is quite different in practice. The displacement of the driver on impact is in the horizontal direction, particularly when the driver is seated in front of the steering wheel which is obliquely disposed to him as well as to the direction of displacement and impact. Thus, the ideal situation as far as impact protection is concerned is not realizable per se.
The French patent No. 1,090,586 discloses an impact protection device wherein in correspondence to the wheel rim deformation the protecting device becomes vertically oriented to meet the horizontally accellerated driver. The device however is very complicated, expensive and does not dissipate a sufficient amount of impact energy which feature, however, is the primary prerequisite for the prevention of injuries.
Another approach to the problem is to provide for a deformable steering wheel support on the column so that upon impact the angle of the steering wheel increases. Such an arrangement provides for some improvement but it requires that the steering wheel is no longer operatively connected to the spindle in the instant of impact, but in just that moment the drive may carry out an evading maneuver which is being interrupted when the connection between wheel and spindle breaks away. Thus, it is definitely a drawback to construct the protection device or feature in a manner which causes the vehicle to be no longer steerable in the emergency situation.